<!DOCTYPE html>
<html>
 <head>
    <title>计算器</title>
    <meta charset="utf-8" />
    <link rel="icon" href="favicon.ico"/>
    <meta name="viewport" content="width=device-width" />
</head>
<body>
  <input id="num1" /> * <input id="num2" />
  <button onclick="jiSuan()">=</button>
  <input id="num3" />


<script>
function jiSuan(){
  num3.value = num1.value * num2.value;
}
</script>
</body>
</html>